I don’t think that’s possible. Submodule1 and Submodule2 are just top level modules. Maybe I don’t understand what you mean by submodules?
I just did a Package the other day where I have Contractors, Workorders and Invoices. Theoretically there is a hierarchy where Contractors would be at the top and Workorders and Invoices would be “sub modules” but it really doesn’t make a differnce. All three modules are just “modules”. How you relate them to one another governs how the are implemented.
My structure is similar to this.
What I want to do is, on navigation bar i don’t want to see them on one list, but inner lists like i added an example.